This invention relates to subscription management in messaging systems.
Publish/Subscribe (or Event Notification) is a well-known messaging pattern where clients interested in information available from a source “subscribe” to the source. When information is available the source then “publishes” the information to the client (which is commonly and hereafter referred to as the “sink”).
There are two common variants of this pattern:
a) The “direct” case, where the sink is registered directly with the source. In this pattern the subscriber identifies each source it is interested in, and then registers a separate subscription with each. It only receives messages from sources with which it has registered.
b) The “brokered” case, where the sink is registered with an intermediary “broker”, not with the true source. The true source publishes information to the broker, which then forwards the information to the sink.
In the brokered case (b) the subscriber does not have to be aware of the identity or location of the true source (publisher), since it never interacts with it directly. The brokered case also has the characteristic that a sink registered against the broker will receive messages from any source (publisher) which is sending relevant messages to the broker. In some situations, this may be exactly what is wanted. However, in some applications (e.g., systems management) the sink might only be interested in messages from a particular set of sources. For example, the sink might be a monitoring application that only wants to monitor 3 out of a set of 60 similar resources.
The direct case (a) allows the sink to control exactly which source(s) it gets messages from. However it can result in a lot of logical connections (if there are m sources and n sinks, we have a total of n*m connections), and it requires each source to maintain a list of subscriptions and each source to distribute messages to multiple recipients.
A need therefore exists for a system and method for subscription management in a messaging system wherein the above mentioned disadvantage(s) may be alleviated.